Automated floor wrenches, and in particular spinner wrenches, for drilling rigs are known. These existing devices do have, however, deficiencies and shortcomings. Most devices are known to have two hydraulic rams opposed to each other, each ram pushing against a pair of spinning rollers to contact, grip and spin the drilling pipe or other tubular. The spinning torque is transferred from the spinning roller to the pipe by means of tangential friction force which is, by definition determined by a coefficient of friction and the resulting gripping forces acting along the lines connecting centers of each roller and the drilling pipe.
A problem with previous devices is that, depending on the direction of spinning the tubular (make-up or break-out), a component of the tangential force associated with active torque will either be positive or negative relative to the gripping force produced by the hydraulic ram. If positive, the “active force” will add-up to the “ram force” and the roller will have good grip with the pipe. If negative, the quality of grip will be diminished and the roller may slip under high torque. Of the two rollers on the single ram, one will always have good grip in the direction of make-up while the other will have good grip in the direction of the break-out, the other roller of the pair will likely not have a good grip.
Maximum spinner torque will typically be determined by the resulting friction force of the two rollers, one on each opposing ram, with unfavourable sum of the forces produced by hydraulic ram and by active torque.
It is, therefore, desirable to provide an automated spinner wrench for a drilling rig that overcomes the shortcomings of prior art devices.